SELECT idprojets, SUM(nbr) as count_commandes
FROM plans
GROUP BY idprojets
) AS CC
ON p.id = CC.idprojets
LEFT JOIN (

SELECT idprojets, COUNT(*) AS count_averifier
FROM files
GROUP BY idprojets
WHERE cfiles.folder = 1 AND cfiles.bat_valid = 0
) AS CA
ON p.id = CA.idprojets
LEFT JOIN (

SELECT idprojets, COUNT(*) as count_modif_nohide
FROM files_modif_title
WHERE statut = 7 AND hide = 0
GROUP BY idprojets
) AS CMN
ON p.id = CMN.idprojets
LEFT JOIN (

SELECT idprojets, COUNT(*) as count_modif_hide
FROM files_modif_title
WHERE statut = 7 AND hide = 1
GROUP BY idprojets
) AS CMH
ON p.id = CMH.idprojets
LEFT JOIN (

SELECT idprojets, COUNT(*)
FROM files
WHERE folder = 2 AND bat_valid = 0
GROUP BY idprojets
) AS CBA
ON p.id = CBA.idprojets
LEFT JOIN (

SELECT idprojets, COUNT(*)
FROM files
WHERE folder = 2 AND bat_valid = 1
GROUP BY idprojets
) AS CBV
ON p.id = CBV.idprojets
WHERE
p.idstatut IN (3)
AND p.deleted = 0
GROUP BY p.id
ORDER BY p.datecreate DESC;

Thanks to what you said, the main problem was the 6 SELECT are embedded in the SELECT clause. These are evaluated for each record put together by the application so it executes 1500 x 6 = 9000 queries!
By doing this I had 9001 queries and now only 7 since subqueries are evaluated only once at runtime. Is that correct ?